1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a digital gamma correction system and method capable of reducing a tact time, using a non-linear interpolation scheme.
2. Discussion of the Related Art
Recently, various flat panel display devices capable of reducing the drawbacks of a cathode ray tube, namely, weight and volume, have been developed. Such flat panel display devices include a liquid crystal display (LCD) device, a field emission display device, a plasma display panel, a light emitting display device, etc.
Of such flat panel display devices, the LCD device displays an image by controlling the light transmittance of liquid crystals in accordance with a video signal. In the LCD device, gamma characteristics are exhibited. That is, in accordance with the voltage level of the video signal, the gray level of the image is not varied in a linear manner, but varied in a non-linear manner. This is because the light transmittance of liquid crystals is varied in a non-linear manner in accordance with the voltage level of the video signal, and the gray level of the image is varied in a non-linear manner in accordance with the light transmittance of the liquid crystals.
In order to prevent the image from being degraded due to such gamma characteristics, the LCD device varies the intervals of voltage levels of video signals, using gamma correction voltages. In other words, in the LCD device, gamma correction voltages, which have different voltage levels in accordance with the voltage levels of the associated video signals, are added, as offset voltages, to the voltage levels of the video signals, respectively, to achieve a correction of gamma characteristics.
In order to achieve a correction of gamma characteristics, accordingly, LCD devices of the related art use, in the manufacturing stage thereof, a gamma corrector to conduct a measurement of brightness, and to correct gamma characteristics in accordance with the results of the measurement. In other words, as shown in FIG. 1, the brightness of a liquid crystal panel displaying an image in accordance with an external input signal is measured. Based on brightness values respectively corresponding to different gray scales, a contrast ratio and gray curve is created. Using the contrast ratio and gray curve, gamma reference voltages are set.
For the gamma correction to set gamma reference voltages, a multi-break point correction and a “look-up table”-based correction, which use an analog circuit or a digital circuit, are generally known. Although the “look-up table”-based correction method, which uses a digital circuit, was known as having a problem of a increased circuit size as compared to other methods, this problem has been reduced in accordance with the recent IC integration improvement. Since the “look-up table”-based correction method has an advantage of a high correction accuracy, the “look-up table”-based correction method using a digital circuit has mainly been used.
FIG. 2A shows the correction results obtained when the brightness of a liquid crystal panel is measured for 256 gray levels of a 8-bit bit code, and is then linearly interpolated for 10 bits. FIG. 2B shows the correction results obtained when the brightness of a liquid crystal panel is measured for 46 gray levels of a 8-bit bit code, and is then linearly interpolated for 10 bits. FIG. 2C is the correction results obtained when the brightness of a liquid crystal panel is measured for 25 gray levels of a 8-bit bit code, and is then linearly interpolated for 10 bits.
As shown in FIGS. 2A to 2C, when the number of detection gray levels to measure a brightness variation occurring between adjacent ones of gray levels increasing sequentially in a full white mode is reduced, the number of interpolation sections increases. When the gray levels increase sequentially, and the number of measurement points are large, as shown in FIG. 2A, the interpolation based on measured data has a gently-increasing gradient. However, when the number of measurement points is reduced, as shown in FIG. 2C, the number of interpolation sections increases because the number of measurement data is reduced. As a result, a step is generated at each measurement point.
Although it is possible to supply gamma correction data suitable for a liquid crystal panel by increasing the number of detection gray levels, an increase in tact time occurs in this case. On the other hand, when a linear interpolation is carried out under the condition in which the number of detection gray levels is reduced to reduce the tact time, there may be a problem in that it is impossible to estimate a brightness to be corrected at each gray level, due to irregular output voltage characteristics of a data driver.
Furthermore, there may be a problem in that a degradation in brightness occurs because it is impossible to supply suitable gamma correction data in accordance with the characteristics of the liquid crystal panel, for which gamma voltage are to be corrected.